Heat exchanger



y 15, 1969 c. A. BEURTHERET I 3,455,376

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1969 c. A. BEURTHERET 3,455,376

HEAT EXCHANGER Filed Aug. 22, 1967 4 $heets $heet 2 c. A. BEURTHERET3,455,376

July 15, 1969 HEAT EXGHANGER 4 Sheets-Sheet 3 Filed Aug. 22, 1967 4Sheets-Sheet 4 C. A. BEURTHERET HEAT EXCHANGER July 15, 1969 Filed Aug.22, 1967 United States Patent Int. Cl. F28d 15/00; F28f 7/00 US. Cl.165-1 16 Claims ABSTRACT OF THE DISCLOSURE A heat transfer surfacehaving grooves formed therein has a forced circulating heat removingliquid confined between this surface and a guide wall, the flow ofliquid being essentially in a direction transverse to the longitudinaldirection of the grooves.

The present invention concerns improvements in methods and devices forheat exchange between a wall and a liquid circulated on contacttherewith. It is more especially concerned with devices of this type inwhich the transfer of an intense thermal flux is effected essentially bylocal vaporization of liquid on contact with the hot wall, andrecondensation of the vapor thus formed in the mass of the circulatingliquid.

It is known that local vaporization is a fundamentally random andunstable phenomenon, susceptible to give rise to an irreversibleoverheating or burnout, leading normally to the destruction by localfusion of the exchanger wall. The burn out occurs if the source fo heatimposes a density of thermal flux which is greater than a critical flux,the vaule of which depends on the nature of the liquid used. By loweringthe temperature of the liquid contacting the exchanger wall, theappearance of this destructive phenomenon will merely occur at a higherthermal flux; it will not eliminate it.

For a long time, the best procedure recommended to increase the thermalflux in exchanges having circulating liquid consisted in avoiding theoccasional formation of boiling points on the hot wall. To this end,there has been employed overpressure, which increases the boiling pointof the liquid, and moreover, turbulent flow, which quickly tears awaythe forming bubbles. This latter comprises the use of obstacles such asturbulence creators, secured either to the exchanger wall or theauxiliary wall, to guide the flow of liquid in a narrow space,tangential to the exchanger surface. Thus, on anodes of electronic tubesor on nuclear fuel elements cooled by circulation of liquid, obstaclesin the form of ribs arranged transverse to the liquid current areformed. These ribs must be of small height and far enough away from eachother so that the creation of nests of bubbles will not occur, whichcould be considered as establishing hot points capable of triggering theburnout phenomenon. If it is desired to designate by throats theintervals between ribs, these throats are thus wider than they are deep;recent research work has confirmed this practice in recommending,moreover even accentuating this ratio of dimensions in making the widthof the throats up to ten or even twenty times their depth. In theseconditions, the depth is then smaller than a millimeter, and the entireheat exchanger surface operates practically isothermically.

In the thus improved exchangers having induced liquid circulation, it ispossible to permit a particular boiling operation, namely, surfaceboiling. In this, the vapor bubbles which form are nearly immediatelycondensed in the cold liquid violently sweeping the exchanger sur- "iceface. Especially under high pressure, this phenomenon contributes toincrease the density of flux admitted before burn out appears; but it isonly obtained on essentially isothermic surfaces, which preventsincreasing, to any extent, the surface of the exchanger by ribs or wingsparticipating in the transmission of the heat.

The increase in thermal dissipation by the improvements described doesnot satisfy all technical needs. Additionally, they have thedisadvantage of requiring a high liquid pumping force due to the verystrong turbulence.

In one field of research, in contradistinction to the above, the work ofthe applicant has resulted, since 1950, in very advantageous embodimentsfollowing from the systematic use of intense boiling, rendered possibleby a particular shape of the exchanger wall. The active surface thereofis increased by the presence of dissipating extensions, and theseextensions are dimensioned, as a function of the thermal conductivity,so that essentially anisothermic extensions of the exchanger surface arepresented to the liquid. The temperature gradient which is establishedon these surfaces maintains a stable vaporization condition calledcomplex vaporization. It concerns an artificial phenomenon, resulting inthe reciprocal stabilization of two phenomena which are naturallyunstable: for example, the method of succession of different forms ofvaporization as a function of the temperature of the wall (in accordancewith the Nukiyama curve) and the evolution in time of the temperatureitself in the presence of these forms of vaporization. This complexvaporization, as well as the means permitting it to form, has beendescribed in an article by the inventor, published at Comptes RendusAcad. Sc. Paris, volume 259, pages 519 to 522, July 20, 1964,Thermocinetic.

Improvements likewise due to the applicant have permitted exchangersusing complex vaporization to become even more effective. In aparticular type of exchanger, the exchanger wall comprises parallel ribsseparated by narrow, deep throats. This exchanger is capable oftransmitting a thermal flux several times greater than the critical fluxof the liquid, and this even if the liquid is already at its boilingtemperature. Its performance is even more increased in the presence of acooler liquid, by natural convection. Rapid circulation forced on theliquid pushing the dissipation of this exchanger even highor as inexchangers having induced circulation.

Experiments have shown that increase in speed of circulation does notresult in a predictable increase in the dissipation, particularly whenthe liquid flow is high in volume and speed. Test results do notcorrespond to supposed extrapolation of performances of the same devicein its natural convection functioning.

The improvements proposed by the invention concern all devices for heatexchange between a wall and a liquid by local evaporation, accompaniedby a recondensation in the mass of moving liquid, in which a heattransfer surface of the heat exchanger wall is formed with depressions,or grooves, in particular in the form of throats, which is exposed to aforced liquid circulation in a confined space, limited by a guide wall.

SUBJECT MATTER OF THE INVENTION The depth of the depressions or throatsis chosen greater than the distance separating their opposed edges;contrary to prior practice liquid is forcibly circulated in a directionof flow which is transverse to the longitudinal direction of thethroats, that is to say, a direction forming locally angles comprisedbetween 45 and preferably between 60" and 90, with the longitudinaldirection of the throats.

The invention is based on the resulting differing paths of flowpresented to the liquid from the entry to the outlet of the device,namely a first path essentially external to the overall geometric volumeof the exchanger wall and a second path essentially internal to thisoverall volume, and formed by the assembly of throats. Common sensesuggests that the most effective heat exchange would be obtained whenthe liquid flow through the second path is as large as possible, thepassage through the throats ensuring, at first blush, intimate contactbetween the liquid and the wall, whatever be the form of the throats.But, in an exchanger in which the exchanger wall comprises throats whichare deeper than they are wide, the invention as defined above, proposesthe contrary, namely, to create a main flow path exteriorly of the walland the throats, in the confined space, limited by the overall surfaceof the wall of the exchanger and the guide wall. In other words, if thetwo flow paths which have just been defined are considered as beingdistinct, the path constituted by the overall assembly of throats in theheat exchanger in accordance with the invention, will have a largehydrodynamic resistance relative to the path defined by the confinedspace, between the heat exchanger wall and the guide wall.

Specific embodiments of the invention will now be described by way ofexample with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view, the wall being shown partly removed toreveal the structure of the exchanger wall therebeneath, of a heatexchanger with a plane exchanger wall;

FIG. 2 is an enlarged section of a part of the exchanger of FIG. 1 in aplane perpendicular to the exchanger wall and arrow 11 of FIG. 1;

FIG. 3 is an elevational view of a heat exchanger comprising acylindrical wall provided with helichordal throats, forming the anode ofan electronic tube, a part of the casing of the exchanger being removed;

FIG. 4 is a part sectional elevation of a heat exchanger comprising anexchanger wall provided with circular throats, the exchanger wall andflow director elements being shown in elevation, the remainder of thedevice being shown in section;

FIG. 5 is a fragmentary section of a heat exchanger comprising a roundedconical exchanger wall provided with circular throats;

FIG. 6 is a section through a heat exchanger comprising a cylindricalexchanger wall provided with throats parallel to its axis, this sectionbeing taken on the line BB of FIG. 7; and

FIG. 7 is a section through the heat exchanger shown in FIG. 6 taken onthe line AA of FIG. 6.

In the drawings, like reference numerals designate like parts.

The heat exchanger shown in FIGURES 1 and 2 is constituted by anexchanger wall 1, a guide wall 2, disposed parallel to the wall 1 and ata short distance 2 therefrom, a liquid distribution chamber 3, providedwith an inlet tube 4, a collecting chamber 5, provided with an outlettube 6, and two lateral closing walls 7 and 8. The exchanger wall 1comprises a rectangular metal plate, for example, in copper, and itsheat transfer face which is visible in the figures comprises a networkof depressions in the form of parallel throats 9, separated by ridges orribs 10. As is shown in FIGURE 2, the depth b of these throats isclearly greater than the distance d separating their edges. The chambers3 and 5, which are arranged along the two opposite edges of theexchanger wall 1, communicate with the space comprised between this wall1 and the guide wall 2. The throats form angles of less than 45 witheach of these two edges. A flow of liquid entering through the tube 4thus forms, between the exchanger wall 1 and the guide wall, a sheetflowing in one direction, designated by the arrow 11, which issubstantially that of the lines connecting the chambers 3 and 5 theshortest way. The direction of flow thus forms, with the longitudinaldirection 12 of the throats, an angle comprised between 45 and Only asmall proportion of the output of liquid is diverted in the direction 12of the throats and flows thereinto. In the example shown, the throats donot themselves discharge into the chambers 3 and 5, their entry beingprevented by a part of a casing 13 of these chambers. As a varient ofthis arrangement, discharge can be effected into one or both chambers,but in both cases, the hydrodynamic resistance of the direct flow pathfrom the distribution chamber to the collecting chamber is less thanthat offered by the assembly of the network of liquid flowing in thethroats. In FIG. 1 there is also shown, in a very schematic manner,outer accessories, ensuring the circulation of liquid in a closedcircuit. The liquid discharging from the outlet tube is cooled in thesecondary chamber 14, of known construction, and reinjected by a pump15, into the inlet tube 4. The installation comprises, moreover, areservoir 26, if desired pressurized, and conventional safety devicesnot shown.

The heat exchange process being effected in the device of FIGURE 1 isexplained with reference to FIG. 2. Arrows 16 symbolize the heat fluxentering by the inlet surface 17 of the wall 1. A small part of thisheat is exchanged by direct conduction between the terminal parts 18 ofthe sides 10 and the liquid which circulates rapidly on contacttherewith in the main flow path 19, between the entire surface 25 of theexchanger wall and the guide wall 2. However, for the larger part, theexchange is effected in the throats 9 by vaporization of the liquidwhich they contain, by a complex boiling operation stabilized by thegradient of temperature which is established on the sides of the ribs10, and this with a mean density of flux in the neighborhood of thecritical flux, the value of which no longer constitutes a limit.Assuming that the liquid is water under an absolute pressure of twoatmospheres (one atmosphere of overpressure) for which the boilingtemperature is 120 C., that the temperature of this liquid is already upto at the moment when it reaches the throat shown in the center of thefigure, and that the mean speed in the space 19 is several meters persecond. In such conditions there are found, for example, in the end zone18 of the ribs a temperature in the neighborhood of C. and on a zoneextending along their sides, between the points 20 and 21, temperaturesranging from 135 to 250 C. favoring complex boiling. Lower down, towardsthe base 22 of the throats, the temperature is even higher and givesrise to a purely film like vaporization. There is schematicallyrepresented the vapor film 23 which rejoins the zone 2221 in which alltypes of vaporization coexist. The vapor 24 thus formed, at atemperature of C., escapes at high speed out of the throat, transverselyto the main flow direction of the liquid, symbolized by the arrows 11.There results an almost immediate condensation by mixing in a turbulentmanner, transferring to the liquid the latent heat of the vapor and, ofcourse, the quantity of heat of smaller amount, corresponding to thedifference between its own temperature and that of the liquid. The twosuccessive exchange processes, vaporization-condensation, alreadyco-exist in the throats themselves but, in fact, the boiling takes placeessentially at the base and on the sides of the throats, while thecondensation is produced near the opening, and essentially in thejunction zone with the liquid flowing in the space 19, on the outside ofthe exchanger wall.

In the present improved exchanger device, the liquid to be vaporized inthe depressions of the exchanger wall is introduced thereinto bybranching off from a small part of the main flow which is arranged tooccur outwardly of the wall 1. This branching results on the one handfrom the component of speed which the flow can present in the preferreddirection of the depressions-the longitudinal direction 12 of thethroats in the example of FIGURE l and, on the other hand, in theturbulence of the liquid in duced due to the component of its direction11, transverse to the depressions. This latter fact is only due from thenecessary branching, if the flow direction no longer PQS.

sesses a component in the longitudinal direction, which would be thecase if, in the example of FIG. 1, the angle were to be 90. It is aboveall the angular deviation between the direction of current of the liquidand that of the throats which ensures to exchangers, constructed inaccordance with the invention, its superiority over those of the priorart, in which the throats in themselves conducted a large amount ofliquid current.

To arrive at the concept of the present invention, the followingreasoning was taken into consideration:

(a) The respective quantities of liquid necessitated by the twoconsecutive heat exchange processes, the vaporization and therecondensation, are very different. In fact, the boiling uses thevaporization heat of the liquid, while for the condensation, it is thespecific heat of the liquid which is concerned. For example, if theliquid is water, its latent heat of vaporization is greater than 500calories. while its specific heat is one calorie per C. It can be seenthat, even if an overall heating of 50 C. of the liquid crossing throughthe exchanger is admitted, the boiling phenomenon only requires puttinginto use a tenth part of the total output. In the prior art exchangers,there has been circulated, through the throats, an output several timesgreater to that necessary for vaporization.

(b) A very intense circulation invoked in the throats of the boilingexchangers of the prior art is not only superfluous but detrimental. Atoo rapid flow of liquid longitudinally imposed in the throats,moreover, if it is turbulent, tends to tear out the bubbles of vaporwhich form on their walls. Such an effect has been sought in exchangersconstructed for functioning with changing of phase; but, in exchangersin which a temperature gradient stabilizes boiling, this violent actionof the liquid current on the surface of the exchanger is not onlysuperfluous but undesirable, as it upsets the establishment of a complexvaporization operational condition.

In the devices constructed in accordance with the invention, thesedifficulties are avoided, because a minor part of the total output canpass longitudinally through the throats, and the major part of theliquid flows in directions which are essentially transverse to thethroats. In the FIG. 1 embodiment, the main required direction of flowis obtained by the arrangement, along the two opposite edges of the wall1, of a distribution chamber 3 and of a collecting chamber 5. Othermeans will be described with reference to the examples shown in FIG-URES 3 to 7. It has been ascertained for all values of the angle ongreater than 45, an improvement in performance is felt with respect toprior art exchangers, that above a=60 the present device presents anotable improvement and that the best results are obtained for anglescomprised between 80 and 90". Even for a=90, the feed of the throats isstill sufficient for the needs of vaporization up to operationalconditions of dissipation which are extremely high. This latter resultis explained by the fact that, in the present exchanger, high externalcirculation speed can be applied without effecting an excessive flow inthe throats. The high turbulence of the liquid which results then makesa quantity of liquid, sufiicient for the needs of the vaporization,divert towards the interior of the throats.

The external appearance of these exchangers is superficially similar tocertain prior art devices having liquid circulation without phasechange; but for the reasons which have been stated, they permit thetransference of densities of flux five to ten times greater than thosepermitted for these prior art devices, and this with a reduction of theoutput of liquid and of the power of the pump, the liquid being able tobe taken to a high output temperature, slightly less than its boilingtemperature, under the applied pressure.

It is interesting to note that the present exchangers do not have thetendency to retain tartar from the use of calcinated water. It has beenfound experimentally that tartar deposits are spontaneously eliminatedby the current of Water. It would appear that this property is due tothe combined effects of the gradient of temperature in the throats andof the turbulent flow in their immediate neighborhood.

The width e of the space in which the main flow is confined is not verycritical but, when determining this Width, there must be taken intoaccount that the efiiciency of heat exchange by condensation isincreased with the speed and the turbulence of the liquid incirculation. A speed of several meters per second is already sufficientto ensure good performance. As the angle a approaches the speed may beincreased. Keeping speed constant requires choice of a width e whichincreases proportionally to the length of the main flow path, since thenecessary output is proportional to the power to be dissipated, and thusto the length of the exchanger wall in the main flow direction. Therehave been obtained good results with widths 2 equal to where L is thelength of the main flow path and k a number between 0.3 and 3. Whateverbe the value of k, the temperature received at the outlet of theexchanger can be in the neighborhood of its boiling temperature, forexample, in the region of 100 C. for water under normal atmosphericpressure, and C. for a pressure of 2 atmospheres. From this there resultthe following points of view for the choice of the factor k:

For relatively large values of k, the hydrodynamic resistance of thedevice and consequently the loss of heat are small; a high output ofliquid is heated little in contact with the exchanger wall. For example,water with flow of 1 liter per minute and per kilowatt, is heated by 15C. Moreover, such conditions are very advantageous for a circulation ofdistilled water in a closed circuit, as the temperature of the liquidcan be fairly high in the entire circuit and the slight necessarylowering of the temperature is then obtained in a secondary, simpleexchanger such as a ventilated radiator.

On the contrary, for relatively small values of k, the hydrodynamicresistance is high, thus compatible with small outputs which have highheating; for example, of 75 C. with flow of water of 0.2 liter/ min./kw. The inlet temperature must, in this case, be fairly low, so that,for example, town water can be used without reuse, since only smallquantities are needed; further, there is obtained as a byproduct somevery hot water which can be put to various uses.

In so far as the dimension of the throats and of the ribs which separatethem are concerned, the general relation b d is preferred. It is furtherdesirable to obtain on a large portion of the surface of the sides andof the throats a gradient of temperature extending between suitablelimits to provide for complex boiling, in other words, operation basedon the Nukiyama curve should be on the first ascendent leg, thedescendent leg and possibly even a portion of the second ascendent leg.This is achieved by using the following dimension formula:

where b is the depth of the throats, defined previously and measured incentimeters, a the mean width of the straight section of the ribsmeasured in centimeters, c the thermal conductivity of the constituentmaterial of the exchanger wall, measured in watts/cm., degreecentigrade, and m a numerical factor of the order of 1, preferablycomprised between 0.7 and 1.8. For the Width d of the throats, there areadvantageously adopted values which are less than preferably less thanof their depth b thus defined. Similar dimensions, although for heatexchangers with recondensation, have already been given previously bythe applicant.

In the case of a relatively high width e of the main flow path, forexample of several mm. an advantageous arrangement, likewise covered bythe invention, consists in cutting off the ends of the ribs separatingthe throats in the form of crenellations. This arrangement locallyincreases the turbulence of the liquid in the opening region of thethroats. Moreover, it accentuates the specific effect sought by theinvention, namely, supplying a sufficient quantity of liquid in thethroats without resulting in a uselessly high flow in the direction oftheir length. In the same way the ribs can be cut in a direction whichis substantially orthogonal, by a reduced number of draining members orchannels, which contribute to the feeding of the throats withouteffecting a flow in the direction of their length.

FIG. 3 shows a heat exchanger constructed in accordance with theinvention, the exchanger wall 1 of which, in cylindrical form,constitutes the outer anode of an electronic tube 27. The guide wall 2forms, with the distribution chamber 3 and the collecting chamber 5, acasing by the open end of which there is introduced the anode of theelectronic tube until a flange 28 surrounding the anode abuts against awater-tight joint 29, itself mounted on a ledge 30 in the said casing.Wing nuts, such as 31, 32, ensure the connection and the watertightnessof the assembly. The exchange device thus constructed presents again thefollowing differences with respect to those of FIG. 1; the throats havea rectangular section and form parallel helices coaxial with the wall of1; the throats discharge not only into the distribution chamber 3 butalso into the collecting chamber 5; finally, the main direction of flowsubstantially transverse to the direction of the throats, is ensured bythe joint effect of the chambers 3 and 5, disposed at the ends of thecylindrical guide wall 2, and of a series of direction blades 33,disposed parallel to the axis of the device in the confined space 19.These blades can be fixed either to the guide wall 2 or to the exchangerwall 1.

The exchanger shown in FIG. 4, serving likewise to cool the anode of anelectronic tube, presents with respect to the proceeding example thefollowing differences: the ribs are disposed circularly around theanode, and the bases of the throats are rounded. The main flow isdirected to be slightly inclined with respect to the generatrices of thecylindrical exchanger wall, by a series of blades 34, extending, as seenobliquely, between the exchanger wall 1 and the guide wall 2. In theexample shown, the guide wall does not constitute the complete envelopeof the device. It is surrounded by a spaced sleeve 35. A dilatableelastic body 37, for example, in an outlet tube 6 inserted in its flatbase. The heated liquid, discharging from the chamber 5, thus passesthrough the annular space between the wall 2 and the sleeve 35. Adilatable elastic body 37, for example, in the form of a hollow rubbertoroid kept in place by a grid 38 is located in this space. Such anelastic body deadens and even eliminates certain abrupt pressurevariations which can accompany the condensation in the turbulent systemin the confined space.

In the exchanger shown in FIGURES 3 or 4, the throats can, for example,present a width of d of 2. mm. and a depth b of 7 mm. The width a of theribs can likewise be 2 mm. and the distance e between the ribs and theguide wall 2 may be 0.3 to 3 mm. Under these conditions, the changerwall, present an inlet surface for heat of 150 cm. is capable ofcontinuously dissipating more than 250 kw., with a water flow in theorder of one liter per second, the water temperature at the outlet beingof the order of 100 C.

FIG. 5 shows an exchanger, the exchanger wall 1 of which constitutes theanode of an electron beam tube. In accordance with a known technique,the impact surface for the electrons, thus the heat receiving surface 17of the wall 1, is in approximately conical form, electrostatic ormagnetic means being provided for diverging the electronic beams 39 soas to give a good distribution of the thermal load on the surface 17,The Wall 1 comprises outer throats 3 disposed in circular formation. Thedistribtution chamber 3 and the outlet tube 6 are arranged in such amanner that the liquid flows along the generatrices of the conical wall,thus at an angle on of with respect to the direction of the throats. Thedistance between the exchanger wall 1 and the guide wall 2 increasesfrom the base of the cone towards its apex, so that the flow speed issubstantially the same along the whole exchanger surface. Thecirculation of the liquid can be established at random in the directionof the arrows or in the opposite direction.

The heat exchanger shown in FIGURES 6 and 7 possesses, as in theexchangers shown in FIGURES 3 and 4, a cylindrical exchanger wall butwith the difference that in that exchanger, the two ends of thecylindrical body to be cooled are outside the heat exchange device, anarrangement which would be adopted, for example, for cooling thecylinders of internal combustion engines. In the exchanger shown inFIGURES 6 and 7 the throats 9 are arranged parallel to the axis of thewall 1 and present as do the ribs 10 which separate them, a section oftriangular form. Around the wall 1 and at a constant distance from thespherical surface 25, there is disposed a guide surface 2 with whichthere are associated a distribution chamber 3, provided with an inlettube 4, and a collecting chamber 5, provided with an outlet tube 6. Thelower lateral walls 40 and 41 of the distribution chamber are concave soas to inject the liquid tangentially into the confined space 19. Due tothis arrangement, the main flow of liquid is constituted by an annularsheet in rotational movement around the exchanger wall, thusperpendicular to the direction of the throats 9. The flow of this liquidin circular motion can be greater than that entering by the chamber 3and leaving by the chamber 5. It is not necessary for these two chambersto be disposed in diametrically opposite regions of the guide wall 2 asin FIGURES 6 and 7 shown by way of example only.

The heat exchanger in accordance with the invention has been describedin structures to cool electronic tubes and parts of thermal motors. Theinvention may also advantageously be applied to different apparatus, inwhich intense thermal energy must be removed, for example, to parts ofchemical reactors and to nuclear fuel elements. In certain of itsapplications, there can be grouped together several of these parts inthe same casing, for example, several cylinders of a thermal motor orclusters of nuclear fuel elements. The casing of the device can be usedto constitute the guide wall or a part thereof, other means for guidingbeing disposed inside the assembly for directing the main flow in therequired direction relative to the throats of each of the exchangerwalls. In the case of curved walls, for example, cylindrical on s, theconvex as well as the concave surface can form the outlet surface forheat. In particular applications Where two heat exchange walls face eachother, these can be disposed in such a manner that each serves as aguide wall for the other.

I claim:

1. A heat exchange arrangement to transfer heat from a heated wall to acirculating heat removing liquid by local evaporation accompanied byrecondensation in the mass of the liquid, comprising a heat transfersurface formed with a plurality of longitudinally extending throatshaving side walls;

a guide wall adjacent said heat transfer surface to confine said liquidbetween said heat transfer surface and said guide wall, the depth ofeach said throat being greater than the distance separating the edgesbetween any one pair of side walls of said throats;

means to forcibly direct said liquid over said heat transfer surface ina direction of flow which, with respect to the longitudinal direction ofsaid throats, forms an angle a of from 45 to 90;

and an inlet and an outlet for said liquid forcibly circulated betweensaid transfer surface and said guide wall in said direction.

2. A heat exchange arrangement according to claim 1, wherein said liquidflow directing means comprising a distribtuion chamber arranged adjacentsaid inlet and a collecting chamber adjacent said outlet, said chambersbeing contiguous with a confined space limited by the heat transfersurface and the guide wall, 'and extending in a direction which isbetween parallel and 45 with respect to said throats, whereby thedirection of flow will be essentially over said throats.

3. A heat exchange arrangement according to claim 1, wherein thetransfer surface is cylindrical and the throats are of helical formarranged between the distribution chamber and the collecting chamber.

4. A heat exchange arrangement according to claim 1, wherein said liquidflow directing means comprises guide blades disposed in the spaceconfined by the heat transfer surface and the guide wall.

5. A heat exchange arrangement according to claim 1, wherein the angle ais from 80 to 90 whereby the direction of said flow will be essentiallytransverse to said grooves.

6. A heat exchange arrangement according to claim 1, wherein said heattransfer surface is a surface of revolution and the throats are formedcircularly and coaxially with respect thereto.

7. A heat exchange arrangement according to claim 1, wherein said heattransfer surface is cylindrical and the throats are formed on aplurality of helices.

8. A heat exchange arrangement according to claim 1, wherein said heattransfer surface is cylindrical and said throats are formedlongitudinally thereof.

9. A heat exchange arrangement according to claim 1,

wherein said throats have straight sections, the mean width of which isless than /3 the depth of the said throats.

10. A heat exchange arrangement according to claim 9, wherein the depthof the throats b and the mean width of the sides a which separate themare defined by the relationship:

where b and a are expressed in centimeters, c designates the thermalconductivity of the constituent material of the heated wall expressed inwatts/centimeterx C., and m is a numeric factor of the order of 1comprised between the limits 0.7 and 1.8.

11. A heat exchange arrangement according to claim 1, wherein thedistance separating the guide wall from the overall surface of theexchanger wall is equal to:

art) where L is the mean length of the main flow path and k a numericfactor of the order of 1 comprised between the limits 3 and 0.3.

12. A heat exchange device for heat transfer from a heated wall to aforced circulation heat removing liquid by local evaporation accompaniedby r condensaticn in the mass of the circulating liquid, wherein theheat transfer surface of the heat exchanger wall is formed with throats,and exposed to the forced circulating liquid, confined by a guide wall,characterized in that:

the depth (b) of the throats (9) is greater than the distance (d)separating their two edges and the device comprises means forciblycirculating a major part of the liquid over said surface and in adirection of flow which, with respect to the longitudinal direction (12)of the throats (9) forms an angle at between and 90.

13. Heat exchange device according to claim 12 wherein the angle a is inthe range of from to whereby the direction of said flow will beessentially transverse to said throats.

14. In a method of removing heat from a heat-exchange surface having aplurality of substantially parallel deeper than wide grooves formedtherein, including the step of circulating a heat exchange fluid incontact with said surface, the improvement comprising the step ofcontacting the interior of said grooves with heat exchange fluid toremove heat from the walls defining said grooves by local evaporation,while forcibly circulating liquid heat-exchange fluid over theheat-exchange surface to re-condense said evaporating heat-exchangefluids into the mass of said circulating liquid fluid.

15. Method according to claim 14 wherein the steps of contacting theinterior of said grooves and recondensing said fluid includes a step offorcibly circulating said liquid fluid over said surface in a directionessentially transverse with respect to said grooves and forming an anglewith the major extent of said grooves of from between 45 to 90.

16. Method according to claim 15 wherein said step of circulating saidliquid fluid includes the step of circulating said liquid fluid 'at anangle with respect to the grooves of from between 80 to 90.

References Cited UNITED STATES PATENTS 2,969,957 l/1961 Beurtheret fl65-74 X 3,046,429 7/1962 Beurtheret 74 X 3,235,004 2/1966 Beurtheret165-185 2,098,380 11/1937 Engelmann et al. 313-20 X 2,863,078 12/1958Prado 31324 FOREIGN PATENTS 1,349,387 12/ 1963 France.

ROBERT A. OLEARY, Primary Examiner ALBERT W. DAVIS, Assistant ExaminerUS. Cl. X.R.

